Cytology is a branch of biology dealing with the study of the formation, structure, and function of cells. As applied in a laboratory setting, cytologists, cytotechnologists, and other medical professionals make medical diagnoses of a patient's condition based on visual examination of a specimen of the patient's cells. A typical cytological technique is a “pap smear” test, in which cells are scraped from a woman's cervix and analyzed in order to detect the presence of abnormal cells—a precursor to the onset of cervical cancer. Cytological techniques are also used to detect abnormal cells and disease in other parts of the human body.
Cytological techniques are widely employed because collection of cell samples for analysis is generally less invasive than traditional surgical pathological procedures such as biopsies, whereby a tissue specimen is excised from the patient using specialized biopsy needles having spring loaded translatable stylets, fixed cannulae, and the like. Cell samples may be obtained from the patient by a variety of techniques including, for example, by scraping or swabbing an area, or by using a needle to aspirate body fluids from the chest cavity, bladder, spinal canal, or other appropriate area. The cell samples are placed in solution and subsequently collected and transferred to a glass slide for viewing under magnification. Fixative and staining solutions may be applied to the cells on the glass slide for preserving the specimen for archival purposes and for facilitating examination.
It is generally desirable that the cells on the slide have a proper spatial distribution, so that individual cells can be examined. A monolayer of cells is typically preferred. Accordingly, preparing a specimen from a fluid sample containing many cells typically requires that the cells first be separated from each other by mechanical dispersion, fluidic shear, or other techniques so that a thin, monolayer of cells can be collected and deposited on the slide. In this manner, the cytotechnologist can more readily discern abnormal cells. The cells are also able to be counted to ensure that an adequate number of cells have been evaluated.
Certain methods and apparatus for generating a thin monolayer of cells on a biological slide advantageous for visual examination are disclosed in U.S. Pat. Nos. 5,143,627, 5,240,606, 5,269,918, and 5,282,978, the disclosures of which are expressly incorporated herein by reference.
Two commercially successful apparatus manufacturing in accordance with the teachings of one or more of these patents has been marketed as the ThinPrep™2000 and ThinPrep™ 3000 Processors (the “ThinPrep™ Processor”) by Cytyc Corporation, located in Boxborough, Mass. During this commercial process, a gynecologic sample is collected using a broom-type or cytobrush/spatula cervical sampling device. Then, the sampling device is rinsed into a vial containing PreservCyt® transport medium. The sample vial is then capped, labeled, and sent to a laboratory for slide preparation. At the laboratory, the vial is placed into the ThinPrep™ Processor, which under control of the instrument's microprocessor, performs the following procedures.
First, the ThinPrep™ Processor uses a portable sample collection device to disperse and collect cells from the liquid sample contained within the sample vial. The sample collection device comprises a disposable plaster filter cylinder, which is introduced by the ThinPrep™ Processor into the liquid sample, and a non-disposable plastic filter cap, which the ThinPrep™ Processor uses to interface with the filter cylinder. The ThinPrep™ Processor generates a negative pressure pulse that draws fluid through the sample collection device, and collects a thin, even layer of diagnostic cellular material on the filter cylinder. The ThinPrep™ Processor constantly monitors the rate of flow through the sample collection device during the collection process to prevent the cellular presentation from being too scant or too dense. The ThinPrep™ Processor then generates a positive pressure pulse that deposits the cellular material on a glass slide. The slide is then analyzed to determine whether the sample is positive or negative for a specified disease.
During the sample collection process, a portion of the liquid sample often comes in contact with the filter cap. Because the filter cap is designed to be non-disposable, and thus reused, it must be thoroughly washed to remove all of the liquid sample that adheres to the filter cap. If the filter cap is not properly washed, cells, microorganisms, proteins and other substances can be transferred from one sample to a subsequent sample, thereby cross-contaminating the samples. As a result, the diagnostic results of each specimen may be compromised. To prevent such contamination, a thorough sterilization protocol is currently followed by technicians who operate the ThinPrep™ Processors.